reproject-crs-geojson

Small package to reproject the vertex coordinates of a GeoJSON between coordinate reference systems (CRS).

Accepts objects of type Feature, FeatureCollection, Geometry, or GeometryCollection, as well as all geometry types: Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon, and GeometryCollection.

The Turf.js coordEach function is used to iterate through all the object's coordinate pairs and reproject them with Proj4js. Additionally, to make CRS selection easier, proj4-list is added.

Documentation

https://f4gm.github.io/reproject-crs-geojson/

Usage

Install the package

npm install reproject-crs-geojson

Imports

import {
  reprojectGeoJSON,
  getEPSG,
  epsgExist,
  toWGS84
} from "reproject-crs-geojson";

Reproject

The reprojectGeoJSON it does not affect the properties, geometry type or number of vertices, it only converts the CRS.

import { reprojectGeoJSON } from "reproject-crs-geojson";

const Point = {
  type: "Feature",
  geometry: {
    type: "Point",
    coordinates: [1060479.7, 865010.7]
  }
}

const converted = reprojectGeoJSON(
  Point,
  "EPSG:3115",
  "EPSG:4326" // WGS84
);

console.log(converted);

// Expected

// {
//   type: 'Feature',
//   geometry: {
//     type: 'Point',
//     coordinates: [ -76.53327992507303, 3.3753051396728866 ]
//   }
// }

You can also include the string PROJ.4:

import { reprojectGeoJSON } from "reproject-crs-geojson";

const epsg_3115 = "+proj=tmerc +lat_0=4.59620041666667 +lon_0=-77.0775079166667 +k=1 +x_0=1000000 +y_0=1000000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs +type=crs";

const Point = {
  type: "Feature",
  geometry: {
    type: "Point",
    coordinates: [1060479.7, 865010.7]
  }
}

const converted = reprojectGeoJSON(
  Point,
  epsg_3115,
  "EPSG:4326" // WGS84
);

To convert directly to WGS84 (EPSG:4326) you can use the function toWGS84:

import { toWGS84 } from "reproject-crs-geojson";

const epsg_3115 = "+proj=tmerc +lat_0=4.59620041666667 +lon_0=-77.0775079166667 +k=1 +x_0=1000000 +y_0=1000000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs +type=crs";

const Point = {
  type: "Feature",
  geometry: {
    type: "Point",
    coordinates: [1060479.7, 865010.7]
  }
}

const converted = toWGS84(
  Point,
  epsg_3115
);

console.log(converted);

EPSG utils

If you want to know if an epsg code is in proj4-list:

import { epsgExist } from "reproject-crs-geojson";

console.log(epsgExist("foo"));
// false

console.log(epsgExist("EPSG:3115"));
// true

If you need the PROJ.4 string:

import { getEPSG } from "reproject-crs-geojson";

console.log(getEPSG("EPSG:4326"));
// +proj=longlat +datum=WGS84 +no_defs

In theory, according to the specification, GeoJSON objects should be in the World Geodetic System 1984 (WGS 84). However, in many cases, we find it necessary to perform these types of transformations.

This is my first npm package, as well as my first foray into the TypeScript language. I apologize in advance for any mistakes.